1. Field of the Invention
The invention relates to a test structure for testing an integrated circuit with a test unit and a test system. The invention also relates to an integrated circuit having external terminals by means of which the integrated circuit can be operated and tested. The invention furthermore relates to a method for testing an integrated circuit.
2. Description of the Related Art
Integrated circuits are tested several times during and after their fabrication before they are passed on to the customer for further processing. To this end, the integrated circuits are connected to a tester unit both at the wafer level (in the front end test) and in the encapsulated state (in the back end test). The tester unit then drives the integrated circuit, via connecting lines, in such a manner that it is possible to find out utilizing a test method whether the functioning of the integrated circuit corresponds to the desired functioning or whether the integrated circuit has a defect.
The tester unit is configured in such a manner that it applies tester signals having a very high signal quality to the integrated circuit via the connecting lines. The voltage supply for the integrated circuit can also be provided by the tester unit. In this case, stringent requirements are imposed on the voltage constancy of the voltage provided so that the tester unit is able to consistently reproduce defects which have occurred (e.g., detected) during test passes.
In spite of the fact that the integrated circuits are tested several times, defects occur when installing the integrated circuits in the end application, for example, at the customer's premises, even though the defects have not occurred or have not been noticed in the previous test passes. Interestingly, however, defects which lead to the corresponding integrated circuit being rejected but do not lead to defective functioning of the end application are also discovered in the test methods during and after the fabrication of the integrated circuit. It has hitherto not yet been fully understood why application testing in the end application is so effective, by comparison with the fabrication test methods, even if application testing takes place in a system environment, for example in a test environment, other than that in which the integrated circuit is intended to be subsequently used. However, application testing is very time-consuming, and there are no automatic handling systems for carrying out application testing. Since application testing requires a very large amount of time, the test throughput is reduced.